(1) Field of the Invention
The present invention relates to a technique for facilitating the handling of plant meristematic tissues.
(2) Related Art Statement
The breeding of plants has been conventionally achieved by fixing superior characteristics acquired by crossing or the induction of mutation as a specific variety (fixed variety). In addition, techniques such as gene recombination and cell fusion have recently led to an employment.
However, anyone of the techniques requires, for particularly an annual plant, the process in which seeds are gathered from parent plants possessing superior characteristics and these are sown in order to obtain offsprings having the same characteristics as these parent plants. Such a breeding method with seeds requires much labor and time and a particular technique for producing a fixed variety and always involves the danger that the characteristics of the fixed variety once produced will deteriorate as a result of natural crossing.
When a useful variety is established as an F.sub.1 hybrid or obtained by a specific chromosomal pattern such as aneuploidy, heterozygosis of structural mutation, or triploidy, it is substantially impossible to cause certain characteristics to be inherited in the coming generation by seed propagation. In these circumstances, it is necessary to gather new seeds by crossing parent plants for each generation, or to obtain seeds by means of a particular treatment. These methods are complicated and, in some cases, involve the possibility of creating an extremely undesirable situation in that it is necessary to depend upon the supply of useful seeds from a particular institution.
Furthermore, propagation methods with seeds require much labor and time and involve disadvantage in being restricted by the weather and the type of land employed.
A technique of vegetative propagation has been developed for the purpose of overcoming the abovementioned disadvantages, in which meristematic tissues such as somatic embryo, adventitious bud, shoot primordium, or callus which are obtained by culturing parts of the tissue of plant bodies are further cultured to encourage shooting and obtain a plant body. Although in some cases this method causes a change in the number of chromosomes, by selecting the conditions, it is possible to obtain a clone having completely the same character as that of the original plant, whereby it is possible in principle to breed from one parent plant a large number of offsprings for many generations without limit.
These types of meristematic tissues are made by culturing plant tissues or cells in a liquid or solid medium under suitable conditions with respect to nutrients, hormones, temperature and so on.
However, with regard to meristematic tissues made in this manner, there is a technical problem in growing a young plant from the meristematic tissue, which provides one of bottlenecks in the development of the technique on usage of the meristematic tissue. That is, to grow a young plant after the process of the tissue culture, a process is necessary in which the meristematic tissues are separated individually or into an assembly each consisting of a few meristematic tissues in some case, and the meristematic tissue separated then must be carried to and set in the place where the young plant grows up.
The mechanical strength of a meristematic tissue is less than that of a natural seed, and the tissues generally adhere each other because of moisture on their surfaces. Therefore, it is an extremely complicated task to separate the tissues individually and carry them to the process of growing up without any damaging to the tissues. To effect these operations without any damaging to the tissues, it is inevitable under the existing circumstances that meristematic tissues are disentangled and separated individually by hand before being carried to the process of growing up. This is far from being an industrial mass production technique, and is inefficient and laborious.
Methods of realizing a process of growing up meristemsatic tissues other than that in which naked meristematic tissue is used have been proposed, such as that disclosed in Japanese Patent Laid-Open No. 59-102308 in which meristematic tissue is encapsulated in a gel matrix, and that disclosed in Japanese Patent Application No. 60-277695 which corresponds to U.S. application Ser. No. 939,514 filed Dec. 9, 1986 in which meristematic tissue is coated so that it is easy to handle, and in that form, the meristematic tissue can be sown directly in a field. In these cases also, it is necessary to previously separate the tissues individually. In addition, it is difficult to perform the above treatments, since mechanical effects such as friction and shock inevitably occur in the process in which the meristematic tissue is encapsulated in a gel matrix or is coated with certain material, which tend to damage the meristematic tissue.
To coat meristematic tissues, it is preferable to employ a tumbling type or a fluidizing type of coating apparatus for production on an industrial scale. However, the coating work performed by using one of these types of apparatus often involves a drying process, so that water contained in the meristematic tissue is evaporated during this process, and there is a risk of the meristematic tissue dying. The meristematic tissue also tends to die while being dried if it is not speedily carried to the next process after it has been made by liquid cultivation and is separated from the liquid culture medium. For this reason also, it is difficult to handle meristematic tissue in a conventional process.